In the signal transmission over a noisy channel, when the dominant channel noise is independent of the transmitted signal, a flat transmit spectrum results in an optimal performance. If the channel noise is signal dependant, performance improvements can be obtained by adding spectral pre-emphasis. Pre-emphasis tends to reduce the average signal amplitudes before the signal dependent impairments, thereby improving performance.
Modems often utilize line probing to select one of a plurality of frequency bands for optimal transmission. A line probing signal processor measures characteristics of the channel based upon a received line probing signal and selects the frequency band to be used for receiving the modulated signal from a remote device based on the characteristics of the channel. The measured channel characteristics are also used to determine a suitable pre-emphasis filter which will be used in the signal transmission.
In the standard of V.34 modem, eleven different kinds of pre-emphasis filters are defined. Thus, there is a need for a method for selecting a pre-emphasis filter during line-probing wherein the method provides efficient filter selection with minimized computation.